package postgres

import (
	"context"
	"database/sql"
	"time"

	_ "github.com/lib/pq"

	"bugs.watch/agent/internal/aggregate"
)

// Collector queries PostgreSQL status each sample interval.
// All queries run under a 3-second timeout; any failure is silently skipped.
type Collector struct {
	db *sql.DB
}

func New(dsn string) (*Collector, error) {
	db, err := sql.Open("postgres", dsn)
	if err != nil {
		return nil, err
	}
	db.SetMaxOpenConns(2)
	db.SetMaxIdleConns(1)
	db.SetConnMaxLifetime(5 * time.Minute)
	return &Collector{db: db}, nil
}

func (c *Collector) Name() string { return "postgres" }

func (c *Collector) Close() { c.db.Close() }

func (c *Collector) Collect(window *aggregate.Window) {
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()

	// pg_stat_database is readable by any user for their own database.
	var numBackends, maxConn int
	err := c.db.QueryRowContext(ctx,
		`SELECT d.numbackends, s.setting::int
		 FROM pg_stat_database d, pg_settings s
		 WHERE d.datname = current_database() AND s.name = 'max_connections'`,
	).Scan(&numBackends, &maxConn)
	if err == nil && maxConn > 0 {
		window.AddDBConnPct(float64(numBackends) / float64(maxConn) * 100)
	}

	// pg_stat_activity requires pg_monitor role (PG 10+); silently skip on error.
	var activeQueries int
	if err := c.db.QueryRowContext(ctx,
		`SELECT count(*) FROM pg_stat_activity WHERE state = 'active'`,
	).Scan(&activeQueries); err == nil {
		window.AddDBThreadsRunning(float64(activeQueries))
	}

	var sizeBytes int64
	if err := c.db.QueryRowContext(ctx,
		`SELECT pg_database_size(current_database())`,
	).Scan(&sizeBytes); err == nil {
		window.SetDBSizeBytes(uint64(sizeBytes))
	}
}